First, I'd stick with the size you have.. 30X10.50X15 is pretty common, allowing you to get a replacement tire if you're away from home, with just the cash in your wallet..
As to a brand, that's a bit harder.. I used to sell tires. Goodyear has discontinued the Wrangler MT (Unwisely, in my opinion) for the newer MTR in your size.. It's very expensive, but is a good tire..
Their lower buck "Extra Grip" is a lesser tire on the highway, but superb on snow (Studdable) and off road conditions. I've seen a forest service vehicle that had to drive 30 miles to the shop with a 1/2" diameter bolt through the tire, with no air loss..
The BFG mahes a very good tire. Their current "KO" incarnation is just now rivalled by Goodyear's MTR..
Also, don't overlook the smaller label tires carried by independents. You won't get much warranty, or road hazard, but you save a bunch of money frequently.. One sold here in Arizona is labelled "Sport King", sold through Discount tire, and other retailers..
I work on some serious offroad vehicles, (Unimogs, and Steyr Pinzgauers) and we have found the cheap Sport Kings work great in the snow, and for rock crawling. Not much in the way of real mud,and a Pinzgauer is hard pressed to do 70MPH, so I cant comment on it's performance there..
Personally, I run 235X75X15LT Goodyear Extra Grips on my 81 Toyota.. They work fine..
Good luck!
Meplat